Decked with tinsel and ornaments, evergreens—farmed or fake—define holiday cheer. Experts say that the best choice is going natural. From a climate-change perspective, you’d have to keep your artificial tree for 20 years before it became a better alternative than the real deal.

“If you like live trees and want to build a tradition, they’re a great choice and not environmentally harmful,” says Clint Springer, a biologist at St. Joseph’s University and a tree expert.

Americans will buy about 21.6 million real trees and 12.9 million artificial ones this holiday season, reports Nielsen Research in partnership with the American Christmas Tree Association, an artificial tree group. (Numbers from the natural tree group, the National Christmas Tree Association, show that consumers bought 28 million natural trees and 8.2 million artificial ones in 2010.)

Most of the artificial variety come from China, so shipping them burns fossil fuels, says Jean-Sébastien Trudel, founder of the Montreal-based consulting firm Ellipsos, which conducted a lifecycle analysis of natural and artificial trees. They’re also made from polyvinyl chloride, which emits volatile organic compounds that can lead to respiratory irritations and distress.

This article originally ran as the Green Guru column in the November-December 2012 issue.